Back plates have been used with conventional dipole magnets to provide magnetic circuits between the two poles of the magnets, where the two poles are on opposite sides of the magnets. Specifically, a typical back plate consists of a cup-shaped piece of metal that is in contact with a first side (also referred to as a surface or face) of a magnet having a pole with a first polarity (in this non-limiting example a North Pole). Side portions of the cup extend around and very near (but not making contact with) the outer boundary of a second side of the magnet having a second polarity (in this non-limiting example a South Pole). As such, the conventional magnet back plate provides a magnetic circuit that causes some or all of the magnetic flux produced by the North Pole of the magnet to be routed near the outer boundary of the South Pole of the magnet, thereby providing a greater magnetic flux density near the South Pole of the magnet. That increased flux density can, for example, increase the holding force when the South Pole and the rim of the cup (i.e., rim of the back plate) are attached to metal. Flux and flux density are well-known concepts to one of skill in the art. A conventional back plate may also be referred to as back iron.
Keepers have been used to preserve the magnetic flux in conventional magnets. Specifically, keepers have been used to provide magnetic paths between opposite poles at both ends of two parallel, conventional bar magnets. Similarly, keepers have been used to provide magnetic paths between opposite poles of conventional horseshoe magnets. Generally, by providing a magnetic path (which may be referred to as a magnetic circuit or a short) between the poles of magnets, the lifetime of such magnets can be extended.